Machines, devices, the latter in particular including also portable devices, and also different kinds of systems may have one or more user interfaces that the operator of the device, or user, can touch in order to control the device. User interfaces most typically have a surface that may be flat or curved.
It is known to detect the touch or presence of a human finger to the surface of a user interface. In particular, touch sensors comprising piezoelectric materials have gained in popularity in the recent years. However, they cannot accurately and reliably detect whether a physical contact between a human finger and the touch sensor exists at a given moment or not.